1. Field of the Invention
The present invention relates to a disk rotating device in a disk drive on which a disk such as a CD (compact disk) or DVD (digital versatile disk) is mounted, and particularly to a disk rotating device that secures a disk, whereby a disk drive using this disk rotating device can be made thinner.
2. Description of the Related Art
Conventional disk rotating devices include the so-called movable type disk rotating device in which a hub (centering member) inserted through the center hole of a disk can move up and down, and the so-called fixed type disk rotating device in which the hub does not move.
FIG. 4 is a sectional view illustrating the structure and principle of a conventional movable type disk rotating device, and FIG. 5 is a sectional view illustrating the structure and principle of a conventional fixed type disk rotating device.
In the movable type disk rotating device T1 shown in FIG. 4, a rotating plate 1 whose circumference is made into a disc-like shape is fastened to a rotating shaft M1 of a spindle motor M. The rotating plate 1 has a recess 1a formed in its center. Inside of the recess 1a is a movable hub (centering member) 2A energized by a coil spring S, which is mounted movably in the vertical (Z) direction. The movable hub 2A has a cylindrical slide part 2a formed on its inner fringe part, and extends in the vertical (Z) direction. The slide part 2a slides and is guided on the circumference of the rotating shaft M1, so that the movable hub 2A is verticallymoveable. The rotating shaft M1 is provided with a stopper 3 on the end (Z1 side) thereof, which prevents the movable hub 2A from falling off in the Z1 direction. The rotating plate 1 has a support plane 1c formed around the entire circumference thereof, which is formed slightly higher than the remaining portion of the rotating plate 1. A disk D is mounted on the support plane 1c. 
On the other hand, in a fixed type disk rotating device T2 shown in FIG. 5, a substantially disc-formed rotating plate 4 is fastened to a rotating shaft M2 of a spindle motor M. The rotating plate 4 has a fixed hub (centering member) 2B projecting from the center thereof. And, in the same manner as the foregoing movable type disk rotating device T1, the rotating plate 4 has a support plane 4c formed around the entire circumference thereof, on which the disk D is mounted. The foregoing fixed hub 2B and the rotating plate 4 are formed into one body by machining or injection molding so as not to be separated from each other.
In either of the foregoing disk rotating devices, the outer circumferential planes 2b of the hubs (movable hub 2A and fixed hub 2B) are tapered. The outer circumference of the hub is inserted through the center hole D0 of the disk D, and thereby the disk D is guided to be centered by the tapered outer circumferential plane 2b. 
Here, the inside diameter of the disk D, for example a CD (compact disk), loaded on the foregoing disk rotating device, namely the diameter of the center hole D0, is 15.0 mm on the specification. The diameter has the allowance on the specification which is from 0.0 through +0.1 mm. Consequently, the inside diameter is specified within the range from 15.0 mm through 15.1 mm. The foregoing specification is the xe2x80x98IEC (International Electrotechnical Communication) 908 Standardxe2x80x99.
The maximum outer diameter xcfx86E of the movable hub 2A shown in FIG. 4 is set larger than the maximum inside diameter (15.1 mm) on the specification of the normal CD. Here, the maximum outer diameter xcfx86E of the movable hub 2A is the diameter of the movable hub 2A on a virtual plane that includes the support plane 1c in the state in which the movable hub 2A is maximally moved in the Z1 direction (the lowering of the hub is 0).
Also, the outer diameter of the head of the movable hub 2A is set smaller than the minimum inside diameter (15.0 mm) on the specification of the CD. Therefore, in the movable type disk rotating device T1, the peripheral edge of the center hole D0 of the disk D necessarily comes into contact with the tapered outer circumferential plane 2b of the movable hub 2A on some position on the outer circumferential plane 2b. Accordingly, the center of the center hole D0 of the disk D coincides with the axis of the rotating shaft M1. In addition, a damper (not illustrated) is lowered to press the disk D in the Z2 direction, whereby the movable hub 2A is lowered in the Z2 direction, and the disk D is held in a space between the damper and the support plane 1c. In FIG. 4, the lowering of the movable hub 2A is illustrated by the symbol h.
On the other hand, in case of the fixed type disk rotating device T2, the maximum outer diameter xcfx86F of the fixed hub 2B is set slightly smaller than the minimum inside diameter (15.0 mm) on the specification of the center hole D0 of the disk D, which is about 14.98 mm, for example. Accordingly, all the disks D of which diameters of the center holes D0 are within the foregoing specification can be mounted on the rotating plate 4, with the fixed hub 2B completely inserted through the center holes D0 of the disks D.
Here, the maximum outer diameter xcfx86F of the fixed hub 2B is the diameter of the outer circumferential plane 2b of the fixed hub 2B, which is on a virtual plane that includes the support plane 4c. 
However, both the foregoing rotating disk devices are intended for CDs. Accordingly, when they are used in a disk drive that can both record and reproduce data to and from disks in which data are recorded with high density, such as a DVD (digital versatile disk), they have the following problems.
FIG. 6 illustrates a distribution chart of inside diameter errors of DVDs, in which the horizontal axis indicates the diameter xcfx86D of the center hole of a DVD and the vertical axis indicates the distribution frequency. A DVD is made of two sheets of laminated discs. From the specification (DVD format), the inside diameter of an individual disc before lamination is 15.00 mm to 15.15 mm, and the inside diameter of a disk after lamination is defined as 15.00 at minimum. That is, the minimum value Dmin of the inside diameter xcfx86D on the DVD specification is 15.00 mm, and the maximum value Dmax is 15.15 mm.
In the conventional movable disk rotating device T1, the peripheral edges of the center holes D0 of all the disks D are made to come into contact with the outer circumferential plane 2b of the movable hub 2A. Therefore, the maximum outer diameter xcfx86E of the movable hub 2A is needed to be set more than the maximum value Dmax of the diameters xcfx86D of the center holes D0 of all the disks D as shown in FIG. 6.
Assuming that the inside diameter of the disk D actually loaded as shown in FIG. 4 is xcfx86D1, the difference of the inside diameter between the maximum outer diameter xcfx86E and the inside diameter of the disk D actually loaded is xcfx86Exe2x88x92xcfx86D1, which is a value indicated by the symbol xcex4 1 in FIG. 6. Further, the maximum difference of the inside diameter xcex4 1max is given when the inside diameter xcfx86D1 of the disk D is Dmin (xcfx86D1=xcfx86Dmin), and it is expressed by xcex4 1max=(xcfx86Exe2x88x92xcfx86Dmin). And, the minimum difference of the inside diameter xcex4 1min is given when xcfx86D1 is equal to Dmax, which is expressed by xcex4 1min=(xcfx86Exe2x88x92xcfx86Dmax). And, as the inside diameter xcfx86D1 becomes smaller, namely, as the difference of the inside diameter xcex4 1 (=xcfx86Exe2x88x92xcfx86D1) becomes larger, the center hole D0 of the disk D comes in contact with the outer circumferential plane 2b at a position closer to the head of the movable hub 2A. That is, the lowering h of the disk D to the support plane 1c of the rotating plate 1 becomes larger. Accordingly, the lowering h is determined by the difference of the inside diameter xcex4 1.
As mentioned above, the inside diameter xcfx86D of a DVD contains a wider error range than the inside diameter of a CD in terms of the specification. Therefore, the difference of the inside diameter xcex4 1 with the maximum outer diameter xcfx86E of the movable hub 2A becomes larger. Accordingly, the lowering h of the movable hub 2A is needed to be set larger than that of the CD. Therefore, it becomes difficult to make thinner the movable disk rotating device T1 and the disk drive that mounts the movable disk rotating device T1. Since the maximum outer diameter xcfx86E of the movable hub 2A is set so that, whenever a disk D of any inside diameter xcfx86D is loaded, the disk D can move down in the Z2 direction, it is required to smoothly slide so as not to produce gallings between the rotating shaft M1 and the movable hub 2A. Accordingly, the cylindrical slide part 2a has to be sufficiently long in the Z direction. This point also makes it difficult to make thinner the movable disk rotating device T1 and the total thickness of the disk drive using this device.
Further, since the coil spring S lifts the movable hub 2A as mentioned above, the stopper 3 of an E ring or the like is needed, which increases the number of the components, which is a problem.
Further, the use of the coil spring S requires a sufficient flexure margin so that the coil spring does not adhere completely during contraction, which is also a restriction against making thinner the movable disk rotating device T1 and the total thickness of the disk drive using this device.
On the other hand, in the fixed type disk rotating device T2, since it is required to pass the center holes D0 of all the disks D without interference around the outer circumferential plane 2b of the fixed hub 2B, the maximum outer diameter xcfx86F of the fixed hub 2B is set smaller than the minimum value Dmin of the inside diameter of the disk D. Therefore, there appears a dislocation (a gap indicated by the symbol xcex 1 in FIG. 6) equivalent to (xcfx86D1xe2x88x92xcfx86F) between the disk D of the inside diameter xcfx86D1 and the fixed hub 2B. This dislocation xcex 1 becomes larger as the inside diameter xcfx86D1 of the disk D becomes larger. And, when the disk D is rotated, since the eccentricity increases in accordance with the dislocation xcex 1, it becomes impossible for the tracking servo system of the optical pickup to follow the track in such a disk as a DVD in which data are recorded with high density, and reproduction becomes impossible. Here, the minimum dislocation xcex 1min appears when the inside diameter of the disk D is the minimum value Dmin, which is given by xcex 1min=(Dminxe2x88x92xcfx86F). And, the maximum dislocation xcex 1max appears when the inside diameter of the disk D is the maximum value Dmax, which is given by xcex 1max=(Dmaxxe2x88x92xcfx86F).
Further, in both CD and DVD, a poor quality disk in which the inside diameter is smaller than 15.0 mm (being the minimum value on the specification) and less than the maximum outer diameter xcfx86F of the fixed hub 2B can be marketed with a rare probability. When such a disk is loaded on the foregoing fixed type disk rotating device T2, the center hole of the disk is caught on the outer circumferential plane 2b of the fixed hub 2B, and the disk cannot be mounted on the support plane 4c but takes an abnormal position. Therefore, there occurs a clamping failure when the damper holds the disk, which is a problem.
The present invention has been made to solve the foregoing problems, and it is an object of the invention to provide a disk rotating device that can make thinner the disk drive to reproduce a CD and to record and/or reproduce a DVD.
Further, it is another object of the invention to provide a disk rotating device whereby a diameter error of the center hole of a disk can be absorbed and the disk can be clamped securely in a normal state.
In order to accomplish the foregoing objects, the disk rotating device of the invention contains: a rotating plate having a support part on which a disk is mounted, which a motor drives to rotate; a centering member provided on the center of the rotating plate and moveable in the direction of the rotational center axis of the rotating plate, which is inserted through the center hole of the disk to thereby center the disk; and an enabling member provided in a space between the rotating plate and the centering member, which projects out the centering member above the support part. Further, when the minimum value of the diameter of the center hole of the disk is given by Dmin and the maximum value thereof is given by Dmax, the maximum outer diameter xcfx86A of the centering member is set within a range of Dmin less than xcfx86A less than Dmax.
In the disk rotating device of the invention, with regard to a disk having the inside diameter within a range between xcfx86A and Dmax, the device functions as the so-called fixed type disk rotating device such that the centering member does not move in the direction of the rotational center axis of the rotating plate. With regard to a disk having the inside diameter within a range between Dmin and xcfx86A, the device functions as the so-called movable type disk rotating device in that the centering member comes into contact with the center hole of the disk and moves. Therefore, the disk rotating device of the invention is different from the conventional movable type disk rotating device in which the centering member moves up and down for all the disks, because the centering member moves down only when a disk is loaded that has an inside diameter between Dmin and xcfx86A. Accordingly, the device of the invention is able to reduce the amount of lowering, and to make thinner the disk rotating device and the disk drive using this disk rotating device.
Preferably, the maximum outer diameter xcfx86A is set within a range of Dmin less than xcfx86Axe2x89xa6(Dmax+Dmin)/2.
Assuming that the variation of the inside diameters xcfx86D of the disks forms a normal distribution as shown in FIG. 6, most of the inside diameters fall near the average value Dave=(Dmax+Dmin)/2. Therefore, when the outer diameter xcfx86A of the centering member is set in the range of Dmin less than xcfx86Axe2x89xa6(Dmax+Dmin)/2, the disk rotating device of the invention is able to function as the fixed type disk rotating device for most of the disks, and to function as the movable type disk rotating device for the disks having an inside diameter less than the maximum outer diameter xcfx86A of the centering member which is within the specification. Therefore, the lowering of the centering member can be made still smaller.
Further, the disk rotating device of the invention contains: a rotating plate having a support part on which a disk is mounted, which a motor drives to rotate; a centering member provided on the center of the rotating plate and moveable in the direction of the rotational center axis of the rotating plate, which is inserted through the center hole of the disk to thereby center the disk; and an enabling member provided in a space between the rotating plate and the centering member, which projects out the centering member above the support part. Further, when the minimum value on the specification of the diameter of the center hole of the disk is given by Dmin and a still smaller diameter than this minimum value Dmin is given by Da, the maximum outer diameter xcfx86A of the centering member is set within a range of Da less than xcfx86A less than Dmin.
When the maximum outer diameter xcfx86A of the centering member is set in such a range, the device of the invention is able to function as the fixed type disk rotating device such that the centering member does not move up and down for most of the disks. Only when an exceptionally poor quality disk whose diameter of the center hole is smaller than the minimum value Dmin is loaded, the device of the invention is able to function as the movable type disk rotating device. Therefore, the lowering of the centering member can be made still smaller, and the disk rotating device and the disk drive can be made still thinner.
Further, the disk rotating device of the invention contains: a rotating plate having a support part on which a disk is mounted, which a motor drives to rotate; a centering member provided on the center of the rotating plate and moveable in the direction of the rotational center axis of the rotating plate, which is inserted through the center hole of the disk to thereby center the disk; and an elastic compressible member of which one face is fastened to the centering member and the other face is fastened to the rotating plate, which projects out the centering member above the support part.
In the above mentioned embodiment, the elastic compressible member preferably is made of a foaming material or a rubber. Also preferably, one face of the elastic compressible member is adhered to the centering member and the other face thereof is adhered to the rotating plate.
The elastic compressible member of the invention is made of a foaming material such as an urethane, which has a specific volume; and it is fastened to both the centering member and the rotating plate by adhesion or the like. Therefore, as compared to the disk rotating device shown in FIG. 4, the stopper 3 is not needed, which reduces the number of the components. At the same time, a large flexure margin as the coil spring requires is not needed, which enables the device to be made thinner. Further, the elastic compressible member preferably possesses an appropriate hardness such that the elastic compressible member is elastically compressed by a clamping force when the damper is lowered, but is not compressed by a pressure of a disk being loaded on the centering member.
Further, since at least one of the centering member and the rotating plate has a recess formed thereon and the elastic compressible member is engaged in the recess, the positioning of the elastic compressible member can easily be accomplished.